Store config files in standardized locations

Currently OpenRGB stores it's config files (sizes.ors and any profile files) in whatever folder OpenRGB was launched from. It might be more ideal to have the configuration files stored, by default, in a standardized location. Perhaps something like $HOME/.config/OpenRGB/ on Mac and Linux and %APPDATA%/OpenRGB/ on Windows would be good default locations to store these configurations.

This should also be paired with a CLI flag to be able to override the storage location. I'm thinking that a command like /usr/bin/OpenRGB --server --conf-dir /var/lib/OpenRGB would be useful for running the OpenRGB server as a systemd service in linux.

This would also resolve the problem where loading a profile at the CLI from a folder other than your current folder can have unexpected/undesired effects. For example, if I run OpenRGB --profile ~/some/path/MyProfile.orp many of my LEDs in that profile will not light up unless the sizes.ors file happens to be in the folder that I am running that OpenRGB command from. Having standardized locations where these files can be located at would resolve that.